1. Field of the Invention
The present invention relates to a polishing apparatus, and more particularly to a polishing apparatus which can be installed in a clean room.
2. Description of the Related Art
Recent rapid progress in semiconductor device integration demands smaller and smaller wiring patterns or interconnections and also narrower spaces between interconnections which connect active areas. One of the processes available for forming such interconnections is photolithography. Though the photolithographic process can form interconnections that are at most 0.5 .mu.m wide, it requires that surfaces on which pattern images are to be focused by a stepper be as flat as possible because the depth of focus of an optical system is relatively small.
It is therefore necessary to make the surfaces of semiconductor wafers flat for photolithography. One customary way of flattening the surfaces of semiconductor wafers is to polish them with a polishing apparatus.
Conventionally, such a polishing apparatus has not been installed in a clean room because dust particles and harmful gas are generated by a polishing operation of the polishing apparatus. Therefore, semiconductor wafers are transported into a clean room by means of a wafer carrier after they are polished by the polishing apparatus installed outside the clean room, and then the semiconductor wafers are processed to form device layers by processing apparatuses installed in the clean room.
However, as described above, high integration in a semiconductor device demands that the semiconductor wafer to be multilayer, and it is therefore necessary to make each surface of the multilayer flat for photolithography. In order to increase productivity of manufacture of the semiconductor device, it is desirable for the polishing apparatus to be installed in the clean room of a semiconductor manufacturing plant.
However, in the case where a conventional polishing apparatus is installed in the clean room, dust particles and harmful gas generated by the polishing operation pollute the air in the clean room.
Further, in such polishing apparatus, abrasive liquid is supplied from a nozzle onto an abrasive cloth attached to an upper surface of a turntable. The abrasive liquid contains abrasive material such as silicon dioxide (SiO.sub.2) or cerium dioxide (CeO.sub.2) having a diameter of 1 .mu.m or less in a liquid.
Furthermore, in order to perform chemical polishing in addition to mechanical polishing, acid or alkali may be added to the abrasive liquid. In such case, acid waste gas or alkaline waste gas or mist is liable to be discharged from the polishing apparatus.
However, in the case where acid waste gas or alkaline waste gas or mist is discharged to the clean room, such gas or mist pollutes the air in the clean room and is one serious cause of lowering the yield of the semiconductor devices.